Thermoregulation

· Body temperature: 37˚ optimum internal temperature

o TOO HOT – cells at risk of denature

o TOO COLD – cells too slow to metabolize enough for survival

· Temperature receptors monitor temperature and are the skin (detects external temperature) and hypothalamus (detects change in blood flowing through)

· Control center (thermoregulatory center) receives input and sends messages to effectors to make adjustments

· Temperature effectors warm up or cool the body.

o Method of heat loss

§ Evaporation of sweat from skin surface

§ Radiation from out of your body (radiant energy)

§ Convection into cold air currents (equilibrium) – hairs lie flat allowing air currents hear the skin so more heat is lost by convection

§ Conduction when you touch something

§ Breathing rate increases so more heat is lost in expired air

§ Excretion

§ Vasodilation the capillaries dilate so more blood is close to the surface to cool

§ Metabolic rate is reduced so less heat is produced

o Method of heat conservation

§ Vasoconstriction is when capillaries constrict so less blood is exposed to surface and close to internal organs so less heat is lost by radiation

§ Sweat production stops

§ Hairs stand preventing air currents getting to skin surface

§ Muscles start involuntary contractions so we shiver to produce heat

§ Metabolic rate increased to generate more heat

o Dependent on

§ Heat gradients (environment against body)

§ Surface area to volume ration (opportunities to loose heat)

o Our first response is voluntary (clothes on or off and moving to warmer or colder areas)

o Our second response is involuntary where heat loss or conversion center in the hypothalamus in the brain is stimulated

§ Some responses conserve heat and others generate it

§ Some responses reduce heat production or transfer heat to the surface

· Hormonal regulation

o Adrenaline is released by adrenal gland (near kidney). This increases metabolic rate and heat production

o Thyroxine is released in long-term exposure to low temperatures and is released by thyroid gland (neck). This causes sustained increases in metabolism.

o The hypothalamus receives stimuli from thermo receptors that temperature is falling

§ It secretes pituitary hormone releasing factors which cause the anterior lobe of the pituitary gland to begin secreting TSH (thyroid stimulating hormone)

§ Which in turn, stimulates the release of thyroxine in the thyroid gland, a hormone which stimulates the increase in metabolic processes, generating heat

· Fever: chemicals called pyrogens released by white blood cells raise the set point of the thermoregulatory center causing the whole body temperature to increase 2-3˚. This helps kill bacteria, inhibits viruses, and explains why you shiver even though you are hot.

· Frostbite: usually your blood carries oxygen to all parts of your body so that your body tissues are kept healthy. As a protective response, when your body is exposed to extreme cold, blood vessels narrow so that blood is diverted away from your extremities to your vital organs to keep your body alive. After some time, this lack of blood supply and oxygen to the skin can start to cause damage to the cells.

· Heat stroke: symptoms of heat stroke include a core body temperature of 41˚, but fainting may be the first sign. Other symptoms include: throbbing headache, dizziness, lack of sweating, red/hot/dry skin, muscle weakness, nausea and vomiting, rapid heartbeat, rapid and shallow breathing, behavioral changes, seizures, unconsciousness

	Created by ameliavincent123 about 11 years ago

Thermoregluation